Solvent extraction



Sept. 7, 1954 D. E. BADERTSVCHER El' Al.

SOLVENT EXTRACTION Filed Sept. 10, 1952 4 Sheets-Sheet l VTER IN1 'EN T0125 MQW/Af E. AferC//EQ AMM@ W. FRANC/5 BY 650/965 6. Jam/50N Sept. 7, 1954 Filed Sept. l0. 1952 WATER D. E. BADERTSCHER El' AL SOLVENT EXTRACTION 4 Sheets-Sheet 2 .EA/C555 Mme www@ gg@ Sept- 7, 1954 D. E. BADERTSCHER ETAL 2,688,645

soLvEN'r ExTRAcTIoN Filed Sept. 10, 1952 4 Sheets-Sheet 4 eNzE/ve 577mm@ 400mm #HMA/5 By 650265 C. Jam/50N patentedA Sept. 7, 1954A UNITED STATES PATENT UFFICI?.

.SOLVENT EXTRACTION -Darwin E. Badertscher, Pitman,Vv and Alfred'W. .Francis and George C. Johnson, `Woodbury, N. J., assignors to Socony-Vacuum Oil Company, Incorporated, a corporation lof NewV York vApplication September 10, 1952, Serial No. 308,828

'19 Claims. vl

This invention is concerned With extraction with certain selective solventsof .various mixtures, and particularly of hydrocarbon mixtures, to separate the mixtures into fractions having diiferent properties.

Numerous processes have been developed for .the separation of hydrocarbons and hydrocarbon derivatives of diiferent molecular conguration by taking advantage of their behaviour with selective agents. For example, aromatics such as benzene, tolueneandxylenes have been separated from hydrocarbon mixtures in which they occur, by adsorption on gels such as silica-alu- .mina composites and the like, by azeotropic disarating aromatics and non-aromatics. .Wilkes- U. S. Patent No. 2,439,534 (1948)-has proposed nine solvents of the same class, i. e., nitriles. All of these solvents are miscible With benzene, a criterion applied by Saunders, which, however, is unnecessary and undesirable since it limits the concentration of aromatic which can be obtained.

Another recently developed solvent extraction involves the use of diethylene glycol, which is not miscible with benzene at ordinary temperatures (-40 C.) but becomes so at 89 C. As described (Chem. Eng., Nov. 1951, p. 242), the extraction may be carried out at a still higher temperature; and, in order to prevent miscibility With benzene, a small amount of Water, of the order of three to eight per cent by Weight, may be added.

-It has now been discovered that a plurality of .fractions ofdifEerent propertiescan be obtained more advantageouslythan with-said prior solvents, by contacting a mixture of aromatic andnon-aromatic hydrocarbons, witha cyclic organic carbonate such .as ethylene carbonate, CzHiCOg, Whichis a cyclic ester. representedV by the formula:

'As a class, thek cyclicv organic carbonates contemplated herein are representedby thegeneral formulae:

. and

.wherein R1, R2, R3 and YR4 are hydrogen or alkyl or alkenyl groups,.and n is a Whole number and is usually three. or four.

It is an object of this .invention,.therefore, to provide an effective means. for separating a multiplicity of lfractions (or compounds) of-different properties from mixtures containing the same. Itis also an object of this invention to provide for the selective-separation of several hydrocarbon fractions of different properties from hydrocarbon mixtures. An important object is the selective separation v of hydrocarbon fractions, diiering in properties, fromhydrocarbon mixtures within the molecular Weight range of about '72 to about .200. A further Aobject yis selectively vto separatebenzene and other aromatics `from mixtures containing the same. Stil-1 another object is selectively to separate non-aromatics, parains and/or napthenes, from mixtures containing the same and aromatics. One other Objectis to provide more highly aromatic .concentrates from hydrocarbon fractions having a relatively .high concentration of aromatics.

Other objects and advantages of the invention will be apparent from the following description.

Inasmuch as ethylene carbonate is a preferred solvent herein, the invention is described below in detail with this particular solvent as an example.

Ethylene carbonate is superior in selectivity to diethylene glycol and to almost all of the nitriles referred to above. Moreover, it makes possible a substantially better recovery of benzene than any one of the aforementioned solvents. Corresponding to the nitriles it is miscible with benzene, but unlike the nitriles it is also miscible with water. The latter feature is an important advantage, since by slight dilution with a diluent the solvent power of ethylene carbonate for hydrocarbon mixtures can be controlled to any desired extent. For example, the addition of four per cent or more of water makes ethylene carbonate incompletely miscible with an equal volume of benzene, so that with such an aqueous solvent practically pure benzene is obtainable, instead of 95.5 per cent benzene obtained by use of the anhydrous ester.

Certain other diluents can be used instead of water to effect the same result. Typical of such diluents are: glycerol, ethylene glycol, pentaerythritol, formamide, formic acid, ethanolamines such as mono, di, and tri-ethanolamines- Certain of these diluents such as glycerol and ethylene glycol, are more advantageous than water, in that long continued Contact of water with ethylene carbonate can cause partial hydrolysis. For this reason, formic acid and bases such as ethanolamines may be less eiicient. When toluene is the desired aromatic to be separated,-a smaller amount of water or other diluent can be used than when benzene is sought; and no diluent is necessary to obtain pure xylenes or higher aromatics.

In general, the diluent should be immiscible with benzene and soluble in the cyclic carbonate, such as ethylene carbonate, to the extent required. All of the diluents mentioned above are miscible with ethylene carbonate except glycerol, which has a solubility in the carbonate of 5.7 per cent by Weight. Mono, diand tri-ethanolamines are substantially equivalent to ethylene glycol in miscibility relationships. Still other diluents which can be used as diluents include: glycerolv monochlorohydrin, acetamide, hydroquinone and resorcinol. Liquids such as diethylene glycol, propylene glycol, trimethylene glycol and lactic acid, all of which are miscible, would not be disadvantageous but would also be of little help, except to lower the melting point of the solvent, because in the quantities recommended they would not render ethylene carbonate immiscible with benzene. It is to be noted that most of the suggested diluents have a high concentration of hydroxyl groups, and all of them are completely miscible with water if liquids, or are exe tremely soluble in water if solids.

The foregoing cyclic carbonates, alone or in admixture with the aforesaid diluents, are effective for extracting benzene, toluene, xylenes and higher monocyclic hydrocarbons, and also methyl naphthalene, tetralin and other polycyclic aromatic hydrocarbons, from mixtures in which one or more of them are present. The hydrocarbon mixture extracted can be from any source containing aromatics, either straight run or cracked. Typical mixtures include: aliphatic hydrocarbonalkyl'oenzene mixtures, catalytically cracked gasolines, catalytically reformed gasolines, iractions from hydrogenated coal and aromatized tei-penes. Any concentration of aromatics is operable. If a single pure aromatic hydrocarbon is desired, one can either distill the mixture to obtain a narrow boiling fraction for the extraction, or separate the desired aromatic from the mixed aromatics by distillation after extraction.

In order that this invention may be more readily understood, typical separation procedures are described below with reference being made to Figures 1 through 3. The processes illustrated are countercurrent extractions of a hydrocarbon mixture with ethylene carbonate at a temperature above its melting point, which can be lowered by a diluent.

Referring to Figure l, a benzene-containing fraction, in line I, is introduced into extractor 2 wherein it is contacted countercurrently with ethylene carbonate added through line 3. The countercurrent extraction is carried out at a temperature of about 40 C. to about 80 C., and at atmospheric pressure. Lower temperatures can also be used. So also can higher temperatures by suitable adjustment of pressure, that is, maintaining suiiicient pressure to keep the system in the liquid state. In the extractor, benzene and any other aromatic present in the charge are extracted and are removed, together with a major portion of the ethylene carbonate, through line 4 to distillation tower 5. This extract is fed to tower 5 at an intermediate point, and benzene concentrate is removed as an overhead product through line 6. If desired, a portion (e. g., twenty to fty per cent) of the benzene concentrate can be returned, through line l, to extractor 2 as an extract reflux.

The bottoms product from still 5 comprises ethylene carbonate and a small amount of hydrocarbons, predominantly aromatics. This product is taken through line 8 to vacuum still 9 wherein this small amount of hydrocarbons is removed from the solvent. Still 9 is operated such that the maximum temperature is below the boiling point of ethylene carbonate at the operating pressure e. g., 10-100 mms. The overhead product from S contains hydrocarbons and a small amount of solvent; this product is taken through line I l] and is returned to still 5 via line ci. Ethylene carbonate, free from hydrocarbons, is taken from vacuum still 9 and from the system through line i I. It can be returned to the system through line 3. In the event that only a partial recovery of the benzene is sought, the material in line 8 can be returned directly to stream 3 without any vacuum distillation.

Returning now to extractor 2, the rainate obtained therein comprises non-aromatics and some solvent. The rainate is removed from extractor 2 through line I2 to washing vessel I3. The raffinate is washed, in a countercurrent operation, with water from line I4 in I3 such that raiiinate free of solvent is removed overhead via line I5. Water containing solvent comprises the bottoms product in I3, and is removed through line I8 to still Il. Water is distilled overhead through line I8 and solvent is recovered via line I9.

The illustration given by Figure 1 applies for ethylene carbonate used alone or used with such diluents as ethylene glycol and glycerol.

When ethylene carbonate is used with water as the diluent, a modication such as shown by Fig-- ure 2 is followed. A charge containing aromat ics-for example, a benzene fraction-is led in from line ZI to an intermediate section of extractor 22. This fraction is extracted countercurrently with ethylene carbonate containing Water,

essi-6245 which is lintroduced to extractor 22 throughline 25. Benzene and any other aromatics-present in the charge are extracted and are removed from 22 through line 24 to distillation tower 25. A benzene concentrate and water are distilled overhead through line 26, containing condenser 21, to settler 28, wherein water forms a lower layer and from which it is removed through line '29. The benzene concentrate is removed from settler 29 and from. the system through line 3D.- Again. a portion of the benzene concentrate can be used as an extract reflux; thus, it can be returned through line 3| to extractor 22.

The bottoms product from tower 25 isethylene carbonate containing a small amount of water; this is removed through line 32. The solvent thus recovered by distillation of the extract layer (from 22) is effectively stripped of hydrocarbons by the water and can be re-used in the extraction upon proper adjustment 0f its water content to the desired percentage.

Referring now to the ramnate obtained in extractor 22, the raffinate isbrought through line 33 to washer 34. The raffinate contains a small amount of dissolved ethylene carbonate, and is washed with water, from line 35. The rafnate comprising non-aromatics, is removed from the washer through line 36. A water solution of ethylene carbonate is formed in washer 311 and is taken through line 3l tol distillation tower 38. Excess water is removed from the tower (38) through line 39 and ethylene carbonate is recovered for re-use as a bottoms product via line 46.

It is also contemplated that a wash oil-or, more technically correct, a displacement solvent be used in conjunction with ethylene carbonate or with ethylene carbonate and a ydiluent of the type described above. The displacement solvent, typically pentane, is a substance whose solvent properties resemble those of the impurities or contaminants in the fraction being treated, but which is more readily separable from the desired aromatic (e. g., benzene), especially by distillation. Pentane, boiling point 36.0 C., is readily separated from benzene, boiling point 80.1 C.; whereas, a common impurity with benzene, namely, cyclohexane has a boiling point of 80.8 C. and is diicult tdseparate by distillation. In general, then, the displacement solvent used herein is a non-aromatic hydrocarbon which can boil above or below, and preferably below, the boiling point of the desired aromatic. Preferably the displacement solvent is one having a boiling point at least about 20 C. above r or below the boiling point of the desired aromatic or aromatics. Representative displacement solvents used in the separation of benzene are: nbutane, mixed butanes, n-pentane, mixed pentanes, mixed pentanes-pentenes, nonanes, decanes, alkylate fractions containing eight to twelve carbon atoms such as the heavy ends from alkylate gasoline, and turpentine.

Figure 3 illustrates an extraction wherein ethylene carbonate and a displacement solvent, pentane, are used. A benzene fraction in line M is fed to an intermediate section of extractor 42, wherein it is contacted by ethylene carbonate from line d3 and by pentane from line 44. A raiiinate layer comprising non-aromatics, some ethylene carbonate and some pentane, is removed from 42 through line 45, and is treated (notshown) as in Figure 1 whereby a rainate, ethylene carbonate and pentane are recovered. Extract from 42 is taken through line 4B to distilure 1.,..f0r .refovery 0i ethylene etboeeie The overhead "product from tower'l' comprises benzene and pentane. :The latter product is brought through line 59 to asecond distillation 'tower r5t, from which pentane is removed as an overhead product via line 5l and from which/benzene is removed as abottomsproduct via flinef52.

The invention 'is also illustrated by "experimental data obtained withbenzene, n-heptane, and'ethylene carbonate perse' orV Ywith'a' diluent.

These experimental data "are presentedjin the "form of charts, orV more particularly ternary diagrams, identieduhere as `Figures 4to-6. These diagrams can be used tojdetermine: the Ysuitability of a solvent for the desiredrseparation;

'the selectivity of the solvents the range of cornvposition of cyclic carbonate, diluent Aand the mixture to be treated; the number of stages or extractions necessarygto yeirect a separation of desired degree;l etc. The vtie lines show compositions of layersin equilibrium.

Figure 4 represents the system benzene-heptane-ethylene carbonate; Figure 5 representa similar system in which aqueous 'ethylenecarbonate is used, ve per cent of water being' used; and Figure 6 represents a similar system in which ethylene carbonate diluted with 5.2 per cent of ethylene glycol is used. l

Figure 4, at 40 C., is of the commonvhyperbolic type. A straight line from the ethylene carbonate corner (isologous line) through the left ends of the tie lines indicates a concentration of 93 to 95.5 per cent benzene in the extracts. The percentage of benzene in the rafinates, found by a similar isologous line through the right ends of the tie' lines, varies for'a single stage according to kthe concentration of the charge. Countercurrent ,operationl will reduce this percentage to a negligible` amount,the' nurnber of stages requiredhepending o'n theavail able concentration in the charge.

Figure 5 shows that ve per cent of water permits recovery of pure benzene's'incauafter the extract reaches a gross concentration o f/.534 per cent of benzene, the isologous line through the left extremity of the tie lines becomes coincident with the side line. vThe tie lines in this graph are somewhat steeper than in Figure 4.

Figure 6, involving dilution with ethyleneglycol, shows similar relationships. Thefmaximum concentration of benzene in the solvent-'tree extract is about 98.5 per cent with this degreeof dilution. Recovery of pure benzene requires dilution of ethylene carbonate with about 22.6 per cent of ethylene glycol. The phase boundary reveals a reverse curve. The solvent is not miscible with pure benzene between 68.4: per rcent and 94 per cent benzene; but this portion of the diagram is not useful for our purpose, because the other liquid phase is only asmall amount of glycol precipitated ,byn the benzene from the solvent (ethylene carbonate). Such a breakup of the solvent does not take place with water, formic acid, or formamide as diluents because ethylene carbonate has much greater afnity for these diluents than for the hydrocarbons. In this respecuthe latter diluents'are preferable to ethylene glycoland glycerol. y

Additional data has been obtained by extracting mixtures*ofbenzenefand Ii-heptane. 'All of these were single-stagef'bat'chu operations. The

7 ratio of solvent to n-heptane was 1.67 by volume or 3.25 by weight. The distribution of benzene is shown in Tables I through lII below.

8- hexene carbonate and butadiene dicarbonate. The homologs of ethylene carbonate have a higher solvent power and, therefore, are less ap- TABLE I Single extraction stage with ethylene carbonate at 40 C.

Benzene in Layers Benzenglelesolvent Benzene Benzene in Recovery Hyilrlocarbon in Extract arge' Extract Ranate Extract Ralnate Wt. Wt' Percent Wt. Wt. Wt. wr. Percent Percent Percent l Percent Percent 30. 6. 4 17. 5 93 17. 6 53 46. 11 31 94 31. 5 47. 5 56. 13. 41. 5 94. 5 42 42. 3 63. 17.2 5() 95 5l 40.2 68. 22 55. 5 95. 5 57 42.0 72. 59 95. 5 6l 42. 3 76. 33 63 95 65 47.5 78. 37 64 95 66. 5 51. 5 80. 40. 5 66 95 69 5l. 5 81. 42 68 94. 5 71. 5 50. 4

TABLE II plicable for extraction of benzene and toluene,

Single extraction stage 'with 95% ethylene carbonate at '30 C'.

Benzene in Layers Benzene in Solvent Free Benzene ln Hydrocarbon Charge, Wt. Extract, Railinete, Extract, Rafiinate, Percent Wt. Per- Wt. Per- Wt. Per- Wt. Percent cent cent cent The third and fth columns of Table II are identical Minimum amounts of various diluents required to make ethylene carbonate incompletely miscible with an equal volume of benzene, and therefore suitable for recovering pure benzene from a mixture with other non-aromatic hydrocarbons, are given in Table IV below.

TABLE IV Diluent: Percentage, wt.

Water 39 65 Glycerol 4.7 Formamide 17.0 Ethylene glycol 22.6 Formic acid 32.6

In addition to ethylene carbonate, other typical carbonates represented by the general formulae set forth above, and contemplated herein are: propylene carbonate, butene carbonates, allene carbonate, cyclopentene carbonate, cyclobut are applicable for extraction of higher aromatic hydrocarbons such as methyl naphthalene. The olen carbonates, typied by ethylene carbonate, should constitute the major portion oi' the solvent used, for example, at least about seventy per cent by weight.

We claim:

1. The process for resolving a hydrocarbon mixture containing aromatic and non-aromatic hydrocarbons into fractions of different degrees of aromaticity, which comprises: contacting the mixture with a solvent comprising a cyclic organic carbonate selected from the group consisting of allene carbonate and of carbonates represented by one of the general formulae:

wherein R1, Rz, R3 and R4. are selected from hydrogen and alkyl and alkenyl groups, and n is a whole number from 3 to 4, and effecting phase separation of the phases thus formed, an extract phase more aromatic than said mixture and a rafnate phase less aromatic than said mixture. 2. The process dened by claim 1 in which a diluent is used in combination with said solvent, said diluent being characterized by immiscibility with benzene and solubility in said carbonate. 3. The process defined by claim 1 in which a diluent having a high concentration of hydroxyl groups is used in combination with said solvent, said diluent being characterized by immiscibility with benzene and solubility in said carbonate. 4. The process defined by claim 1 in which aqueous ethylene carbonate is the solvent, said solvent containing from about two to about ten per cent by weight of water.

5. The process dened by claim 1 in which ethylene glycol is used in combination with said solvent.

6. The process dened by claim 1 in which glycerol is used in combination with said solvent.

7. The process defined by claim 1 in which a displacement solvent is used in combination with said solvent.

8. The process dened by claim 1 in which pentane is used in combination with said solvent.

9. The process defined by claim 1 wherein the hydrocarbon mixture is one containing benzene and non-aromatic hydrocarbons of similar boiling range.

10. The process dened by claim 1 wherein the hydrocarbon mixture comprises aromatic, aliphatic and cycloparaiiinic hydrocarbons.

1l. The process for resolving a hydrocarbon mixture containing aromatic and non-aromatic hydrocarbons into fractions of different degrees of aromaticity, which comprises: contacting the mixture With a solvent comprising ethylene carbonate, and effecting phase separation of the phases thus formed, an extract phase more aromatic than said mixture and a rainate phase less aromatic than said mixture.

12. The process defined by claim 11 in which a diluent is used in combination with said solvent, said diluent being characterized by immiscibility with benzene and solubility in said carbonate.

13. The process dei-ined by claim 11 in which a diluent having a high concentration of hydroxyl groups is used in combination with said solvent,

10 said diluent being characterized by immiscibility with benzene and -solubility in said carbonate.

14. The process defined by claim 11 wherein the hydrocarbon mixture is one containing benzene and non-aromatic hydrocarbons of similar boiling range.

15. The process dened by claim 11 wherein the hydrocarbon mixture comprises aromatic, aliphatic and cycloparaiiinic hydrocarbons.

16. The process dened by claim 11 in which ethylene glycol is used in combination with said solvent.

17. The process dened by claim 11 in which glycerol is used in combination with said solvent.

18. The process denedby claim 11 in which a displacement solvent is used in combination with said solvent.

19. The process defined by claim 11 in which pentane is used in combination with said solvent.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,917,910 Sullivan July 11, 1933 2,582,883 Myers Jan. 15, 1952 FOREIGN PATENTS Number Country Date 413,307 Great Britainr July 11, 1934 

1. THE PROCESS FOR RESOLVING A HYDROCARBON MIXTURE CONTAINING AROMATIC AND NON-AROMATIC HYDROCARBONS INTO FRACTIONS OF DIFFERENT DEGREES OF AROMATICITY, WHICH COMPRISES: CONTACTING THE MIXTURE WITH A SOLVENT COMPRISING A CYCLIC ORGANIC CARBONATE SELECTED FROM THE GROUP CONSISTING OF ALLENE CARBONATE AND CARBONATES REPRESENTED BY ONE OF THE GENERAL FORMULAE: 